The present invention relates to the field of finger joint prostheses used for replacing phalangeal and metacarpophalangeal joints.
Various diseases, such as post-traumatic arthrosis, evolutive polyarthritis, infectious arthritis and certain rheumatic states lead to a progressive deterioration or destruction of the finger joints. Thus, for a number of years, joint implants or prostheses of various types have been developed in the surgical field in order to attempt to restore the use of the fingers of the hand in patients suffering from such diseases.
The destruction of metacarpophalangeal (MP) and proximal interphalangeal (IPP) joints of the long fingers leads to a therapeutic problem for the hand surgeon which has not yet been completely solved PELLEGRINI V. D., BURTON R. I., Osteoarthritis of the proximal interphalangeal joint of the hand, arthroplasty or fusion, J. Hand Surg. 1990, 15-A,2,194-209). The recovery of functional amplitudes requires the replacement of joint surfaces, no matter whether the joint destruction is the consequence of a post-traumatic arthrosis, the development of an evolutive polyarthritis or an infectious arthritis.
Details will be given of the main solutions envisaged and applied up to now, while on each occasion indicating their disadvantages.
The appearance of silicone implants SWANSON A. B. Silicone rubber implants for replacement of arthritic or destroyed joints in the hand, Surg. Clin. North Am., 1968, 48, 1113-1127), has been subject to certain advances in this field. However, over a period of time numerous complications inherent in the material have appeared such as the fracture of implants, lateral instabilities, lack of strength, residual pain, etc. The reaction to silicone foreign bodies, which is a possible source of autoimmune pathology makes the use thereof arbitrary particularly in the case of young patients EKFORS O. ARO H. MAKI J. AHO A. J. Cystic osteolysis induced by silicone rubber prosthesis. Arch. Pathol. Lab. Med. 1984, 108, 225-227).
The unsatisfactory results with such implants, particularly in post-traumatic cases, have led to research being carried out on other arthroplastic solutions BLAIR W. F., SHURR D. G., BUCKWALTER J. A. Metacarpophalangeal joint arthroplasty with a metallic hinged prosthesis. Clin. Orthop. 1984, 184, 156-163, and CONDAMINE J. L., BENOIT J. Y., COMTET J. J., AUBRIOT J. (in French) Proposal for digital arthroplasty: critical study of the initial results, Ann. Chir. Main, 1988,7,4, 282-297).
Two arthroplasty concepts are possible, namely stressed arthroplasties on the one hand, where the two articulated parts are mechanically joined and semi and non-stressed on the other, where the two parts have no mechanical link.
The problems of lateral stability encountered with non or semi-stressed prostheses have led the applicant to opt for a stressed hinged implant consequently only having a single degree of freedom, namely that of bending-extension.
This hinged implant type raises two problems, namely that of the strength and the reliability of the actual hinge and that of the anchoring of the diaphysed parts, no matter whether or not they are sealed.
Existing arthroplasties are produced from stainless steel and polyethylene or titanium and polyethylene, besides silicone.
As a further illustration of the state of the art reference can be made to FR-A-2 590 794, FR-A-2 605 878 and FR-A-2 620 932. These three documents disclose the use of diaphysed parts or pins for fixing in the medullary channel of the finger bones. The part issue at their common end onto a swivel joint and/or rotation system having one or two degrees of freedom and make it possible to reconstitute a freedom of finger movement which is as close as possible to that given by natural joints.